A digitizer tablet computer has been designed which uses a secondary type or rechargeable battery as the primary power source allowing a user to carry the computer about from place to place and conduct different transactions. Thus one of the main objectives of such design was to prolong the useful life of the battery as much as possible by using power management techniques disclosed in the above related application (2), and by accurately measuring the power status of the battery and accurately indicating to the user how much time remains before the battery will be fully depleted. Such indication thereby not only allows the user to save any critical current data but also to use the computer as long as possible before the battery becomes depleted and has to be recharged or replaced.
Within the prior art, there are many examples of devices that keep track of the charge in a rechargeable battery used within different types of devices. U.S. Pat. No. 4,724,528- J. T. Eaton discloses a "BATTERY CHARGE MONITOR IN A COMPUTER SYSTEM" in which a single microprocessor monitors the battery and accumulates both new charge and consumed charged. Such system appears to be a relatively simple low performance system not involving distributed processing and in particular, not involving any digitizer tablet computer.
U.S. Pat. No. 4,965,738- G. W. Bauer et al discloses an "INTELLIGENT BATTERY SYSTEM" in which a battery pack of a plurality of rechargeable cells has integrated into the pack electronic circuitry, including a CPU and memory, for monitoring the charge status of the battery. Battery parameters are stored and accumulated charge and discharge are kept track of by measuring the battery charge and discharge currents.
U.S. Pat. No. 5,047,961-B. P. Simonsen discloses an "AUTOMATIC BATTERY MONITORING SYSTEM" for use with an emergency standby battery. The monitor keeps track of battery conditions and provides a daily printout thereof. The system also includes a CPU and memory and LCD display.
However, none of the above patents, discloses a battery operated digitizer tablet computer having a high performance, distributed processing system in which a service processor controls operation of a power subsystem microcontroller to monitor and charge a rechargeable battery in the manner of the invention, as describe in detail below.